The invention relates to a method for producing a ceramic layer on a surface formed from a Ni base alloy.
According to the prior art, it is known for example from Yoshiba, M. et al., “High-Temperature Oxidation and Hot Corrosion Behavior to Two Kinds of Thermal Barrier Coating Systems for Advances Gas Turbines”, J. Therm. Spray Tech. 5 (1996), 259-268 that ceramic protective layers can be applied to Ni base alloys, for example by means of plasma spraying. The ceramic protective layers are usually oxide-ceramic protective layers, in particular ZrO2 stabilised with Y2O3 (YSZ). Ceramic protective layers of this type improve the corrosion resistance and the wear resistance of a component coated therewith. Apart from this, such ceramic protective layers are used for thermal insulation of components in turbine and engine construction due to their low thermal conductivity and their high reflecting power.
Contact with hot corrosive media results disadvantageously in a flaking of the ceramic protective layers. Yoshiba et al. (see above) observed in hot corrosion tests that an application of a salt melt formed from Na2SO4 and NaCl to a ceramic layer contributes to an improvement of the adhesiveness.
DE 689 11 363 T2 discloses an object which is produced from a Ni base alloy and which is coated with a ceramic protective layer formed from YSZ. To improve the adhesiveness, one or more intermediate layers is/are first deposited on the object prior to the application of the ceramic protective layer.
Lima, C. R. C.; da Exaltação Trevisan, R.: Temperature Measurements and Adhesion Properties of Plasma Sprayed Thermal Barrier Coatings in Journal of Thermal Spray Technology, 8, 1999, 2, 323-327 discloses a method in which first an intermediate layer formed from a metal and a ceramic and then a ceramic layer containing ZrO2 as a main constituent are applied by means of plasma spraying to a substrate produced from a Ni base alloy.
Guo, H. B.; Vaβen R.; Stöver D.: Atmospheric plasma sprayed thick thermal barrier coatings with high segmentation crack density in: Surface & Coatings Technology 186, 2004, 353-363 discloses a method in which a mixture of a polymer and a ZrO2 stabilised with yttrium is applied by means of plasma spraying to substrate produced from a Ni base alloy. The porous ceramic layer with ZrO2 as main constituent thus produced has an improved thermal cycle stability.
The object of the invention is to overcome the disadvantages according to the prior art. In particular, a method for producing a particularly adhesive ceramic layer on a surface formed from a Ni base alloy is to be specified.
This object is achieved by the features of the invention. Expedient embodiments of the invention will emerge from the features of the invention.